Conventional engine timing systems consist of a crankshaft and corresponding sprocket system which operate an engine with either single or dual overhead camshafts. The operation of a conventional engine system is based upon a chain which extends from the crankshaft to the camshaft (or camshafts) and returns to the crankshaft in an endless loop. The movement of the crankshaft and the chain causes the camshaft to rotate. Alternatively, a separate chain can drive between the two camshafts of each bank of cylinders in a dual overhead camshaft engine timing system. Examples of engine timing systems are shown in U.S. Pat. No. 5,427,580, entitled “Phased Chain Assemblies”, which is incorporated herein by reference.
As the chain extends in an endless loop between the driving and the driven sprockets, such as those located on a crankshaft (driving shaft) and camshaft (driven shaft), the chain forms a “tight” side and a “slack” side. The “tight” side is formed by the tension in the span of chain between the links entering the driving sprocket and the links leaving the driven sprocket. A “slack” side is formed on the other span of chain between the links leaving the driving sprocket and entering the driven sprocket.
The performance and action of the chain differs between the tight and slack sides. A chain tensioner is conventionally used on the slack side of the chain. The tensioner acts to take up or eliminate the slack in the chain. As the engine accelerates or decelerates, the tensioner arm may move closer to the chain to maintain the tension, i.e., eliminate the slack in the chain. The tensioner arm typically includes a convex surface to match the path of the chain. In the use of the chain tensioner on the slack side of the chain, the tensioner arm is subject to vibrations and forces from the sudden acceleration and deceleration of the engine. Such vibration can cause wear on a tensioner arm surface.
In contrast, a chain guide is conventionally used on the tight side of the chain. Such a guide is typically designed to remain fixed, as the chain portion remains tight between the two sprockets. The guide serves to maintain the desired path of the chain between the sprockets.
FIG. 1 depicts a prior art chain guide with tapered side rails. The illustration shows only a single engine bank of the engine timing system. The engine system consists of a crankshaft 20 and corresponding sprocket 21 and a sprocket 31 mounted on camshaft 30. As explained above, a chain guide may be used with other engine timing systems. The key is to use the chain guide on the tight side of an endless chain.
The engine timing system 10 includes chain 40, chain tensioner system 50, and chain guide 1. The engine chain 40 extends from the crankshaft 20 to the camshaft 30 and returns to the crankshaft 20 in an endless loop. The movement of the crankshaft 20 causes the sprocket 21 to rotate which, in turn, causes sprocket 31 and camshaft 30 to rotate.
The crankshaft sprocket 21 is the driving sprocket and thus the tight side 43 of the chain is formed between the links entering the crankshaft sprocket and leaving the camshaft sprocket 31. The slack side 41 is the opposite side of the chain between the two sprockets 21, 31.
The slack side has a chain tensioner system 50. The tensioning system 50 is designed to maintain the tension on the slack side of the chain. The tight side 43 of the chain 40 has a chain guide 1 to keep the chain in position. The chain guide 1 is positioned so that its upper side 12 is against the underside 42 of the chain 40. The chain 40 is forced into motion by the sprockets 21 and 31, resulting in its movement across or through the groove of the chain guide 1 along a direction of travel of the endless chain.
Consideration of information disclosed by the following U.S. Patents, which are all hereby incorporated by reference, is useful when exploring the background of the present invention.
U.S. Pat. No. 5,779,582 entitled CHAIN GUIDE with tapered side rails teaches a chain guide, which will be utilized on the tight side of the chain of an engine system, is designed to reduce the lateral motion of the chain. The chain guide is constructed with raised side rails that taper inward to the center. The slot which guides and controls the chain gradually narrows towards the center.
Japanese patent application JP8004848(A2), entitled TENSIONER ARM AND CHAIN GUIDE, teaches a tensioner arm and a chain guide by which deterioration of properties of engine oil can be prevented.
U.S. Pat. No. 6,322,471, entited CHAIN GUIDE teaches a chain guide which includes an angle-like guide base having a single mounting portion bolted to a mount surface on the interior side of an endless chain and projecting to the exterior side of the chain through a space defined between the chain and the mount surface. A shoe supporting portion of the angle guide base projects perpendicularly from an exteriorly projecting end of the mounting portion and is provided with a plurality of nose locking projections spaced in a direction of travel of the chain. A guide shoe is provided with a plurality of generally hook-shaped resilient locking prongs projecting from a rear surface on a side opposite to a shoe surface. The locking prongs are snap-fitted with the locking projections to attach the guide shoe to the guide base with the shoe supporting portion held between the rear surface of the guide shoe and the locking prongs. The angle guide base is highly rigid and hence is able to suppress vibration and noises generated while the chain is running. The mounting portion of the guide base, which is disposed interiorly of the endless chain, does not increase the overall size of an apparatus to which the chain guide is mounted.
U.S. Pat. No. 6,312,353, entitled CHAIN GUIDE, teaches a chain guide for guiding a chain includes an elongated chain guide body pivotally connected at one end to a fixed support member and having an aperture formed in an opposite end of the chain guide body, and a collar loosely fitted in the aperture in such a manner that a clearance is defined between the chain guide body and the collar at least on that side of the collar which is aligned with a direction of pivotal movement of the chain guide body. The collar is firmly secured to the fixed support member so that the chain guide body is allowed to pivot within the range of the clearance. With the clearance thus provided, the chain is protected against excessive tightening or loosening which may otherwise occur when the chain guide is mounted on the fixed support member.
U.S. Pat. No. 5,665,019 entitled CHAIN GUIDE MOUNTING ASSEMBLY FOR THE REDUCTION OF CHAIN INDUCED NOISE AND VIBRATION IN A CHAIN DRIVEN OVERHEAD CAM INTERNAL COMBUSTION ENGINE teaches a chain guide mounting assembly for reducing chain related noise in a chain driven overhead cam internal combustion engine. The assembly includes vibration isolation means for mounting the chain guide to the engine. Resilient members, fitted within the chain guide, provide the vibration isolation, which, in turn, reduces undesirable chain noise. To prevent undue lateral movement of the chain guide member as a result of the chain force exerted thereon, a rigid sleeve in interference engagement is fitted within bores of the resilient members. As a result, a preload is provided on the resilient members so as to reduce the amount of undesirable lateral movement.
All of the above cited publications have a common characteristic, which is the upper side 12 of chain guide 1 is formed out of a single piece or member. The present invention teaches a chain guide which has an upper side that is formed out of at least two members.